The wide strip mill of the present invention may be utilized to roll any appropriate strip material. The mill, however, is particularly well adapted for cold-rolling of rapidly work-hardening, tough metal such as stainless steel or silicon steel, and particularly such metal strips of wide width and light gauges. As a result, for purposes of an exemplary showing, the mill will be described in its application to the rolling of wide width, light gauge stainless steel, silicon steel and the like.
Heretofore, for the rolling of wide width, light gauge metallic strip, prior art workers have most often turned to the well-known 20-roll mill of the type taught in U.S. Pat. No. 2,479,974. The 20-roll mill comprises a pair of upper and lower work rolls. Each work roll is provided with a pair of backing rolls, three outer backing rolls (the outermost two of which are usually driven) and four large bearing rolls.
Hundreds of such 20-roll mills are in operation throughout the world and demonstrate excellent performance. These 20-roll mills will accept work rolls which are the smallest for a given width of any mill known. Such 20-roll mills, however, are characterized by certain drawbacks. For example, they are very large, complex in construction, very heavy, expensive to manufacture and its tonage output is limited by the capacity of its eight bearing rolls.
The present invention is based upon the discovery that through the employment of pressure elements, an eight-roll mill can be developed which will greatly out-perform the well known 20-roll mill. The pressure elements can be of the type taught in U.S. Pat. No. 4,603,569 (incorporated herein by reference and described hereinafter). The invention also contemplates new and improved pressure elements to be described hereinafter.
The mill of the present invention utilizes upper and lower work rolls, each provided with backing rolls and only one outer backing roll. The two outer backing rolls of the mill are driven. A total of four outer backing rolls and the eight bearing rolls are eliminated. Each of the backing rolls and the outer backing rolls is provided with a plurality of pressure elements evenly spaced along its face, by which both the vertical and horizontal components of the roll separating force are transmitted to the mill housing. The use of the pressure elements is of extraordinary importance because the pressure elements are capable of withstanding pressures substantially greater than the capacity of the bearing rolls of the 20-roll mill.
The mill of the present invention represents a genuine contribution to the art, as compared to the conventional 20-roll mill, in that it can use optimum diameter work rolls and backing rolls, and requires only two driven rolls. The mill is capable of handling substantially heavier roll pressures, thus reducing the number of passes required and considerably increasing the tonage output for the same size mill. At the same time, the mill of the present invention is far simpler in construction, weighs far less than a conventional 20-roll mill of the same size and can be manufactured at a greatly reduced cost.
With increasing demand for wide width, light gauge, rapidly work-hardening strips such as stainless and silicon steels, the more efficient and less expensive mill of the present invention can result in large savings industry-wide.
The improved pressure elements of the present invention utilize polymer bearing surfaces. They are more wear resistant, do not require lubrication and are less expensive to manufacture. Their use is not limited to the improved mill of the present invention. They can find application wherever rolls require backing or support.